SODICITY IN SOUTH AUSTRALIA - A REVIEW

The current knowledge of the nature and distribution of sodic soils in South Australia is reviewed. The agriculturally developed area of Sou th Australia lies south of latitude 32-degrees-S. and is mainly used f or low intensity grazing and dry land cereal/sheep production. A high proportion of the State, including much of the high rainfall area, has soils which are sodic (>6% ESP) through a significant proportion of t he profile but information on the precise nature of sodicity in these soils is limited. Where exchangeable cation data axe available, the an alytical techniques used often did not precisely delineate between sol uble salts in the soil and ions on exchange sites. Therefore, many of the datasets have major weaknesses and may be unreliable. Since many s oils with ESP <6 also show dispersive characteristics typical of sodic soils, there is an urgent need for new sodicity studies relating to d istribution and the criteria (ESP) used to identify dispersive soils. Information on the effect of sodicity on nutrient requirements of plan ts, especially the modern varieties, is scarce both locally and intern ationally, making development of management strategies for economicall y sustainable crop production difficult. Further, many different grade s of gypsum are available in South Australia. Preliminary studies show the presence of impurities drastically influences gypsum dissolution characteristics. More effort is needed to assess the quality and react ivity of South Australian gypsum. Some effort has been directed by lan d managers towards reclamation and management of sodic soils by using both gypsum and lime either separately or as mixtures. However, there is neither a scientific basis for the application of gypsum-lime mixtu res nor crop production data to support such management strategies.